Xref: utzoo rec.birds:2516 sci.bio:3403
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From: keithl@loop.uucp (Keith Lofstrom;;;646-6296)
Newsgroups: rec.birds,sci.bio
Subject: Re: HEAD JERKING OF WALKING BIRD
Message-ID: <1990Aug2.041738.364@loop.uucp>
Date: 2 Aug 90 04:17:38 GMT
References: <1990Jul28.033019.5059@ddsw1.MCS.COM> <1990Jul30.132412.6397@cid.aes.doe.CA>
Organization: Launch Loop, Portland OR
Lines: 16

I got here late; sorry if this has already been suggested:

Birds have small brains, and can't distinguish between their own motion and the 
motion of the predators they are trying to avoid.   If you watch the head closely,
it holds still while the bird's body continues forward, then jerks forward to a
new fixed position.  This feeds a series of stationary images to the bird's brain,
and makes moving objects in the visual field more obvious.

Why doesn't a bird's head move when riding on a shoulder?  Birds didn't evolve
to ride on shoulders;  the built-in reflexes are wrong.


-- 
Keith Lofstrom  keithl@loop.uucp ...!sun!nosun!loop!keithl (503)628-3645
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Power ICs